Embryogenesis and plant regeneration from maize zygotes by in vitro culture of fertilized embryo sacs.

Fertilized embryo sacs of Zea mays were isolated and cultured In vitro. Each explant contained one zygote and 2-4 endosperm nuclei which formed, respectively, embryo and cellular endosperm during the culture. In our double-layer/two-phase culture system, NBM medium (Mòl et al. 1993) supplemented with 0.1-1.0 mg·l(-1) zeatin and 12 % sucrose showed the best results. On this medium, embryos were isolated from 37-54 % of two-week-old explants. They were similar to maize embryos developing in vivo. We have shown that development of stage-2 embryos (according to Abbe and Stein 1954) with two leaf primordia and normally differentiated provascular tissue is possible from the maize zygote in an in vitro culture system. Some embryos with enlarged and deformed scutellum or whole apical parts were also found. Up to 62 % of the embryos germinating on a simple medium regenerated into mature and fertile plants; i.e. 23 % of explants yielded plants. This unproved culture method results in better embryo differentiation and 14-fold increase of regeneration frequency than previous protocol.